T-Mobile has a data only SIM - but it is indeed data only. No SMS, no voice. You can check out the terms on their website (
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AT&T has data packages you can add to its voice SIM. This will let you do your SMS too, of course, and you can just ignore the ability to make calls if you like, although for making local calls it can be very convenient.
CA: SaskTel, Wind postpaid; Rogers, Bell postpaid iPad flex plans; US: T-Mobile postpaid data, prepaid voice; PureTalk (AT&T MVNO) prepaid voice/data; AT&T prepaid iPad plan
Hardware: Too much but notably iPhone 5, iPad Mini Retina LTE, Moto G LTE (N.A. version), iPhone 4. All unlocked.